1. Field of the Invention
The present invention relates to a torque limiter including a magnetic powder clutch which yields to a torque exceeding a specific magnitude, for use in the transmission line of general industrial machines, such as copying machines and wire winding machines, for limiting the torque acting on the transmission line to a specific magnitude.
2. Description of the Prior Art
The construction and functions of a conventional torque limiter for such a purpose will be described with reference to FIG. 7 showing the upper half of the torque limiter in a longitudinal section.
Shown in FIG. 7 are a rotary shaft 1, bearings 2, a cylinder 3 made of a magnetic material, end plates 4 and 5 made of a nonmagnetic material such as brass or a stainless steel and fixedly fitted in the opposite ends of the cylinder 3, respectively, rotors 6 and 7 made of a magnetic material and coaxially secured to the rotary shaft 1, a permanent magnet 8 disposed between the rotors 6 and 7, and coaxially secured to the rotary shaft 1, magnetic powder P such as iron powder filled in a space A within the cylinder 3, and sealing members 9 such as oil seal elements or felt rings for preventing the entrance of the magnetic powder P into the bearings 2. The rotary shaft 1 is supported rotatably in the bearings 2 on the end plates 4 and 5.
The rotor 6, the magnetic powder P, the cylinder 3, the magnetic powder P and the rotor 7 form a magnetic circuit .phi. indicated by a broken line followed by the magnetic flux of the permanent magnet 8. The torque of the rotary shaft 1 is transmitted to the cylinder 3 or the torque of the cylinder 3 is transmitted to the rotary shaft 1 by the agency of the magnetic flux. When the torque to be transmitted exceeds a specific magnitude, the magnetic flux is unable to transmit the torque and allows the rotary shaft 1 and the cylinder 3 to move relative to each other, so that the torque capable of being transmitted by the torque limiter is limited to a valve which is below the specific magnitude.
The conventional torque limiter has the following drawbacks:
(1) In filling the magnetic powder P in the cylinder 3, the magnetic powder P is liable to stagnate in a space B between the outer end surface of the rotor 7 and the inner end surface of the end plate 5 and between the outer end surface of the rotor 6 and the inner end surface of the end plate 4, and hence it is difficult to fill the magnetic powder P satisfactorily in the normal space A between the outer circumferences of the rotors 6 and 7, and the inner circumference of the cylinder 3.
(2) The magnetic powder P is liable to stay in the space B while the torque limiter is stopped and starts gradually migrating to the normal space A after the torque limiter has started rotating, and hence the torque limiter is unable to transmit torque satisfactorily in the initial period of operation.